The invention relates to modified copolymers and terpolymers more particularly usable as multifunctional additives for lubricants. They have antiwear and viscosity index-improving properties.
The basic copolymers and terpolymers consist of ethylene-propylene copolymers and ethylene-propylene-diene terpolymers (EPDM copolymers). According to the invention, they are modified so as to fix sulphur and phosporus.
Ethylene-propylene copolymers and ethylene-propylene-diene terpolymers have long been used for improving the viscosity of lubricating oils. They are prepared by the copolymerization of ethylene and propylene and optionally an unconjugated diene, which can be dicyclopentadiene, 1,4-hexadiene or ethylidene-norbornene, usually followed by a mechanical degradation stage so as to obtain a copolymer having an appropriate molecular weight.
Copolymers modified so as to simultaneously permit the improvement of the viscosity index of lubricating oils and the dispersion of the residues which they are liable to contain in use have already been proposed. Such copolymers are generally obtained by modifying ethylene-propylene copolymers either by grafting nitrogenous dispersant monomers, or by maleinization and reaction with polyamines and/or polyols. The preparation and use of such additives are more particularly described in U.S. Pat. Nos. 4,092,255, 4,146,489, 4,170,561 and 4,175,975, EP-A-225,048 and 4,144,181.
Copolymers or terpolymers modified so as to simultaneously make it possible to improve the viscosity index, disperse residues and provide antioxidant protection have also been proposed. The preparation and use of such additives are more particularly described in U.S. Pat. Nos. 4,668,412, 4,904,404, 4,863,623 and 4,798,678.
In addition, U.S. Pat. No. 4,502,972 describes the preparation and use as an additive for lubricants a polymer obtained by the treatment of an ethylene-propylene-diene terpolymer with chlorine, followed by a reaction with a sodium N,N-dialkyldithiocarbamate.
In general terms, the use of multifunctional additives makes it possible to avoid problems of compatibility of the additives, simplifies the formulation of the lubricating compositions and leads to improved performance characteristics.